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<br />2.2 Hydrology. The dischargeEL u(lE~d for this study were those used <br />in the 197H Flood ]?:i.ain Information Studv and the Flood Insurance Study <br />cur::.-ently being finalized. The d.ischarg"es arE~ shown .in Table One. <br /> <br />TI\.BL.Il CNE: <br /> <br />South Pla"tte RivE~r Discharges <br />at Ste.rlinq, Colora.do <br /> <br />Ret\.::rn Interval <br /> <br />Pl?ak Diflcharge <br /> <br />lO-Year <br />50-Year <br />lOO-Year <br />SOD-Year <br /> <br />IS,OOO c.LfI. <br />!)~j,OOO C.f.EI. <br />134, ODD c. L fl. <br />207,OOD C.LEI. <br /> <br />3. <br /> <br />HYDRAULIC ANALYSIS. <br /> <br />3.1 <br />computed <br />The 1988 <br />uses the <br />gradually <br /> <br />Existing Conditions. Water ~3u:rface profiles and floodways were <br />using the u.s. Army corps of Enqin.eers HEC-2 backwater program. <br />release for IBM compat.i.ble miCJ~ocompu1:er8 was used. The program <br />standard step backwatE!r method and is applicable to Elteady <br />varied flow in natura.l c:hanneln. <br /> <br />The HEC-2 data uBI3d for the Flooel P:.ai::l Information st~udy was obtained <br />from the Co.rps of :~ngineE;!rs computer. a.l:Ghive and was updated to meet <br />existing conditions. Minor adjustments r,.,l'e:~e ma.de t:o the bridge models and <br />some cross sections we:::-e extended. 'l'he "n-' values were a.ssigned based on <br />the field inspection of the area, aerial l?ho1:os acquired from the Logan <br />County ASCS, and engineering judgement. The fJelected values are shown in <br />Tabl'3 Two. All existing agricultural le"E:'H~s in the overbanks were <br />dete,rmined to be failed for the exist:inq conditions a.nd floodway water <br />surf,ice eleva1:ions calculations. Existing conditions water surface profiles <br />are :3hown on Plate 1. <br /> <br />4 <br />